A universal mobile telecommunications system (UMTS) is a third-generation mobile communications system evolving from a global system for mobile communications system (GSM), which is the European standard. The UMTS is aimed at providing enhanced mobile communications services based on the GSM core network and wideband code-division multiple-access (W-CDMA) technologies.
In December 1998, ETSI of Europe, ARIB/TTC of Japan, T1 of the United States, and TTA of Korea formed a Third Generation Partnership Project (3GPP) for creating detailed specifications of the UMTS technology. Within the 3GPP, in order to achieve rapid and efficient technical development of the UMTS, five technical specification groups (TSG) have been created for determining the specification of the UMTS by considering the independent nature of the network elements and their operations.
Each TSG develops, approves, and manages the specification within a related region. Among these groups, the radio access network (RAN) group (TSG-RAN) develops the specifications for the functions, requirements, and interface of the UMTS terrestrial radio access network (UTRAN), which is a new radio access network for supporting W-CDMA access technology in the UMTS.
A related art UMTS network structure 1 is illustrated in FIG. 1. As shown, a mobile terminal, or user equipment (UE) 10 is connected to a core network (CN) 200 through a UMTS terrestrial radio access network (UTRAN) 100. The UTRAN 100 configures, maintains and manages a radio access bearer for communications between the UE 10 and the core network 200 to meet end-to-end quality of service requirements.
The UTRAN 100 includes a plurality of radio network subsystems (RNS) 110, 120, each of which comprises one radio network controller (RNC) 111 for a plurality base stations, or Node Bs 112. The RNC 111 connected to a given base station 112 is the controlling RNC for allocating and managing the common resources provided for any number of UEs 10 operating in one cell. One or more cells exist in one Node B. The controlling RNC 111 controls traffic load, cell congestion, and the acceptance of new radio links. Each Node B 112 may receive an uplink signal from a UE 10 and may transmit downlink signals to the UE 10. Each Node B 112 serves as an access point enabling a UE 10 to connect to the UTRAN 100, while an RNC 111 serves as an access point for connecting the corresponding Node Bs to the core network 200.
Among the radio network subsystems 110, 120 of the UTRAN 100, the serving RNC 111 is the RNC managing dedicated radio resources for the provision of services to a specific UE 10 and is the access point to the core network 200 for data transfer to the specific UE. All other RNCs 111 connected to the UE 10 are drift RNCs, such that there is only one serving RNC connecting the UE to the core network 200 via the UTRAN 100. The drift RNCs 111 facilitate the routing of user data and allocate codes as common resources.
The interface between the UE 10 and the UTRAN 100 is realized through a radio interface protocol established in accordance with radio access network specifications describing a physical layer (L1), a data link layer (L2) and a network layer (L3) described in, for example, 3GPP specifications. These layers are based on the lower three layers of an open system interconnection (OSI) model that is well known in communications systems.
A related art architecture of the radio interface protocol is illustrated in FIG. 2. As shown, the radio interface protocol is divided horizontally into a physical layer, a data link layer, and a network layer, and is divided vertically into a user plane for carrying data traffic such as voice signals and Internet protocol packet transmissions, and a control plane for carrying control information for the maintenance and management of the interface.
The physical layer (PHY) provides information transfer service to a higher layer and is linked via transport channels to a medium access control (MAC) layer. Data travels between the MAC layer and the physical layer via a transport channel. The transport channel is divided into a dedicated transport channel and a common transport channel depending on whether a channel is shared. Also, data transmission is performed through a physical channel between different physical layers, namely, between physical layers of a sending side (transmitter) and a receiving side (receiver).
The MAC layer of the second layer provides a service to an upper layer, namely, an RLC (Radio Link Control) layer, via a logical channel. The RLC layer supports reliable data transmissions, and performs a segmentation and concatenation function on a plurality of RLC service data units (RLC SDUs) delivered from an upper layer.
A radio resource control (RRC) layer located in a lowermost portion of the L3 layer is defined only in the control plane. The RRC manages the control of logical channels, transport channels, and physical channels with respect to establishment, reconfiguration and release of radio bearers (RBs). A radio bearer service refers to a service that the second layer (L2) provides for data transmission between the terminal and the UTRAN. In general, the establishment of a radio bearer refers to defining the protocol layers and the channel characteristics of the channels required for providing a specific service, as well as respectively setting substantial parameters and operation methods.
A Multimedia Broadcast Multicast Service (MBMS) is implemented in the UMTS system as follows. The MBMS refers to a method for providing a streaming or background service to one or more terminals by using a downlink-exclusive MBMS bearer service. One MBMS service is made up of one or more sessions, and MBMS data is transmitted to multiple terminals through the MBMS bearer service only when a session is ongoing.
The UTRAN 100 provides the MBMS bearer service to terminals using an RB. Two types of RBs used by the UTRAN 100 are a point-to-point RB and a point-to-multipoint RB. The point-to-point RB is a bidirectional RB, including a logical channel DTCH (Dedicated Traffic Channel), a transport channel DCH (Dedicated Channel) and a physical channel DPCH (Dedicated Physical Channel) or a physical channel SCCPCH (Secondary Common Control Physical Channel).
The point-to-multipoint RB is a unidirectional downlink RB, including a logical channel MTCH (MBMS Traffic Channel), a transport channel FACH (Forward Access Channel) and the physical channel SCCPCH as shown in FIG. 3. The MTCH is configured for every MBMS service provided in one cell and used to transmit user plane data of a specific MBMS service to multiple terminals.
FIG. 3 illustrates a channel mapping structure of the point-to-multipoint RB. A logical channel MCCH, which is a point-to-multipoint downlink channel, transmits MBMS-related control information. The MCCH is mapped to the transport channel FACH. The FACH is mapped to the physical channel SCCPCH. Only one MCCH exists in one cell.
The UTRAN providing the MBMS transmits MCCH information to multiple terminals via the MCCH. The MCCH information includes a notification message related to the MBMS. Namely, the notification message is an RRC message related to the MBMS. For example, the MCCH information includes a message having MBMS service information, a message having point-to-multipoint RB information and access information indicating that RRC connection is requested for a specific MBMS.
FIG. 4 is a conceptual view illustrating a transmission method of the MCCH information. The MCCH information is periodically transmitted according to a modification period and a repetition period. The MCCH information may be divided into important information and non-important information. The non-important information may be freely changed and transmitted during every modification period and repetition period. The important information may be changed and transmitted only during the modification period. Specifically, the non-important information may repeatedly be transmitted once every repetition period, and modified important information may be transmitted only at a start point of the modification period.
The UTRAN periodically transmits a physical channel MICH (MBMS notification Indicator Channel) to inform whether the MCCH information is updated during the modification period. Thus, when the terminal wants to receive one specific service, it periodically receives the MICH (not the MCCH or the MTCH) before a session of the corresponding service starts. Updating of the MCCH information is related to the generation, addition, change and removal of a specific item of the MCCH information.
When the session of the specific MBMS service starts, the UTRAN transmits an NI (Notification Indicator), namely, an indicator for notifying the terminal wanting to receive the MBMS service that it should receive the MCCH, via the MICH. Upon receiving the NI via the MICH, the terminal receives the MCCH during a specific modification period indicated by the MICH.
The terminal wanting to receive the specific MBMS using the point-to-multipoint RB, receives the MCCH information including the RB information via the MCCH, and establishes the point-to-multipoint RB using the MCCH information. After establishing the point-to-multipoint RB, the terminal continuously receives the physical channel SCCPCH, to which the MTCH is mapped, to obtain data of the specific MBMS transmitted via the MTCH.
FIG. 5 illustrates MBMS service data transmitted via the physical channel SCCPCH to which the MTCH is mapped. The UTRAN discontinuously transmits MBMS data via the MTCH, and periodically transmits the scheduling information via the SCCPCH to which the MTCH is mapped. The scheduling information indicates a transmission interval of the MBMS data, which is transmitted during one scheduling period. Thus, the UTRAN indicates in advance not only the scheduling information but also the transmission period of the scheduling information.
The terminal obtains the transmission period of the scheduling information from the UTRAN, receives scheduling information according to the transmission period of the scheduling information, and discontinuously receives the SCCPCH (to which MTCH is mapped) by using the received scheduling information. Namely, the terminal receives the SCCPCH (to which MTCH is mapped) during a time interval that the MBMS data is transmitted and does not receive the SCCPCH (to which MTCH is mapped) during a time interval that the MBMS data is not transmitted.
The method of determining whether to receive the channel transmitting the MBMS data according to the scheduling information has an advantage that the terminal can effectively receive data. Thus, battery consumption of the terminal can be reduced.
Meanwhile, as shown in FIG. 5, while the MTCH with respect to the specific MBMS is set, the UTRAN transmits an SNI (Secondary Notification Indicator) to the terminal via the SCCPCH (to which MTCH is mapped). When the MCCH information with respect to the specific MBMS is updated, the SNI is used to inform the terminal, which is receiving the MTCH, about whether to update the MCCH information. Accordingly, when the terminal, which is receiving the SCCPCH (to which MTCH is mapped), receives the SNI via the corresponding SCCPCH, the terminal receives the MCCH according to an indication of the SNI, and then receives MCCH information via the MCCH. The SNI can be transmitted or received via the logical channel MTCH or via a different logical channel mapped to the SCCPCH together with the logical channel MTCH.
In the related art MCCH information update notification method, if the MCCH information with respect to the specific MBMS service is to be transmitted through the MCCH, and an MBMS session does not proceed, such as before the session starts or after the session stops, the UTRAN transmits the NI to the terminal via the MICH. If the MCCH information is updated and the MBMS session proceeds, the UTRAN transmits the SNI via the SCCPCH, to which MTCH is mapped.
In order to check whether the MCCH information has been updated, the terminal whose MTCH has not been set receives the NI of the MICH to check whether the MCCH information has been updated. In case that the MTCH of the terminal has been set, the terminal receives the SNI via the SCCPCH, to which MTCH is mapped, and checks whether the MCCH information has been updated.
In the related art control information update notification method, while the MTCH is set, the terminal checks whether the MCCH information with respect to the specific MBMS has been updated by receiving the SNI. However, if the terminal discontinuously receives the MTCH according to the scheduling information, the SNI cannot be received if MBMS data is not being transmitted during discontinuous transmission. Accordingly, a problem occurs because the terminal ineffectively receives the SCCPCH, to which the MTCH is mapped. Consequently, the terminal cannot effectively use its battery. Therefore, what is needed is a control information update notification method wherein the terminal can check whether the MCCH information with respect to the specific MBMS has been updated even during a time interval when the MBMS service data is not being transmitted.